A US watchdog has found no evidence of political bias when the FBI launched an inquiry into the 2016 Trump campaign, despite "serious performance failures".
The US Department of Justice inspector general's report concluded the law enforcement bureau had "authorised purpose" to initiate the investigation.
But it also found applications to wiretap a Trump aide had "significant inaccuracies and omissions".
The 476-page report provides fodder for Trump critics and supporters alike.
Inspector General Michael Horowitz sought to assess the basis for the FBI's surveillance of Carter Page, a former Trump campaign adviser who had lived and worked in Russia.
How did the report criticise the FBI?
The inspector general identified 17 "significant inaccuracies or omissions" when the FBI applied to the Foreign Intelligence Surveillance Court (Fisa) for surveillance warrants to monitor Mr Page's communications.
Mr Horowitz wrote that the errors resulted in "applications that made it appear that the information supporting probable cause was stronger than was actually the case".
The watchdog also found that an FBI lawyer assigned to the Russia case doctored an email from the CIA to a colleague that was used in an application from the bureau to monitor Mr Page.
The attorney "altered an email that the other US government agency had sent" with the effect that "the email inaccurately stated that Page was 'not a source' for the other agency", the report said.
The watchdog also found FBI personnel "fell far short of the requirement in FBI policy that they ensure that all factual statements in a Fisa application are 'scrupulously accurate'".
The report said "so many basic and fundamental errors... raised significant questions regarding the FBI chain of command's management and supervision of the Fisa process".
How did the report back the FBI?
The inspector general found no basis for conservative claims that partisan hostility to Mr Trump had influenced the bureau's probe.
"We did not find documentary or testimonial evidence that political bias or improper motivation influenced the decisions to open the four individual investigations," he said.
Mr Horowitz also did not find that the FBI's mistakes were intentional.
The investigation was opened "in compliance with department and FBI policies", the report said.
Mr Horowitz also found the FBI's use of confidential informants was in compliance with agency rules.